How does chemotherapy affect my chances of becoming pregnant after treatment?

Answer: We always recommend that women use effective birth control during chemotherapy. Since your menstrual cycles can become irregular, you won't know if you're pregnant or if it's just a side effect to the chemotherapy. So it is important to use birth control, because chemotherapy can have harmful side effects to the fetus in the first trimester. However, in the second and third trimester, we can use chemotherapy very successfully with minimal harm to the baby.